Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1994-09-28
1996-07-30
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324306, 324307, G01V 300, G01V 314
Patent
active
055415121
ABSTRACT:
A magnetic resonance system employs a sequence of radio frequency pulses and magnetic field gradients to generate a flow-compensated image of a selected portion of a sample. Flow-compensation is performed with an oscillating readout gradient waveform which is comprised of two components. The first component is a constant amplitude gradient waveform whose amplitude is determined by the desired field-of-view and the bandwidth of the imaging system. The second component is an oscillating waveform whose amplitude, frequency and phase are chosen to obtain the desired degree of flow-compensation. The frequency of the oscillating waveform is typically chosen to match the sampling frequency of the imaging system. In effect, each acquired data point is preceded by the application of a bi-polar magnetic field gradient pulse which causes a phase shift in the acquired signal which is proportional to nuclear spin velocity. The amplitude is typically chosen to cause an incremental phase shift which when repeatedly added to the acquired MR response signal at the sampling rate causes a frequency modulation. This frequency modulation, in turn, induces a spatial displacement of signal intensity in the readout dimension which corresponds to the displacement of spin magnetization during the interval between the phase-encoding and frequency-encoding.
REFERENCES:
patent: 4654591 (1987-03-01), Moran
patent: 4718424 (1988-01-01), Nishmura
patent: 5007426 (1991-04-01), LeRoux
"Elimination of Oblique Flow Artifacts in Magnetic Resonance Imaging" by L. R. Frank, A. P. Crawley, R. B. Buxton, Magn. Reson. in Med. 25: 299-307 (1992).
Darrow Robert D.
Dumoulin Charles L.
General Electric Company
Haynes Mack
O'Shea Sandra L.
Snyder Marvin
Zale Lawrence P.
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